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Does ospf auto summarize interarea networks12/21/2023 If both prefixes have the same metric them both routes will show up in the routing table (and the router will load share traffic to that destination). If you run 2 OSPF processes and if each process learns the same prefix then each OSPF process will attempt to insert its route into the routing table. But each OSPF process will advertise only the routes that are contained in its own database. There is a single routing table for the router which will contain routes from both OSPF processes. Yes the separate OSPF processes have separate OSPF data bases and the separate OSPF processes do not share any data with the other OSPF process unless you redistribute. The only way to have one process advertise prefixes from the other process is to redistribute. each OSPF process will advertise only prefixes from its own data base. each OSPF process will learn its own prefixes and maintain those prefixes in its own database. So each OSPF process will have a unique set of neighbors. an interface can be active in only 1 interface. The implications of running separate OSPF processes include these: The easy way to accomplish this is to run separate OSPF processes, to redistribute routes between processes, and to filter the redistribution to allow only some routes to be redistributed and advertised by the other process. Or perhaps there is a situation where your router will learn certain routes in OSPF but you do not want to advertise some of those routes to other parts of your network. In this case your router knows routes of both customers but will not advertise routes from customer B to customer A. The easy solution for this is to run an OSPF process on the interface connecting to customer A and to run a separate OSPF process on the interface connecting to customer B. But you do not want customer A to see customer B routes. And you want to run OSPF with customer B. And perhaps your router also connects to customer B. Perhaps your router connects to customer A and you want to run OSPF with customer A so that you can support them. There are several reasons why you might choose to run separate OSPF processes. I would answer a couple of things a bit differently from Manish. OSPF will determine what to advertise based on the configured subnets on the interfaces that it includes in its processing. the network statement does not tell OSPF to summarize (there are separate commands to control summarization). the network statement does not tell OSPF what to advertise but tells OSPF what interfaces to process. Then OSPF looks at the subnet defined on that interface (including its mask) and advertises that subnet. When the OSPF process starts it looks at its configured network statements (and the address ranges defined by the address and the mask) and it looks at every interface on the router (that is in up/up state) and if an interface falls into the range defined by a network statement then that interface is included into OSPF. It is the combination of the network statement and the configured interfaces that determine what is advertised by OSPF. It is not just the network statement and it is not just the interfaces on the router that are configured. Let me try to clarify one of the things that you say:"it is not the fact that the network statement under OSPF encompasses the whole range of subnets that determines which LSAs are created and sent, but the actual interfaces that are configured on each router." OSPF 499 is running OSPF on this interface (see the network statement), yet the interface is un-passived out in OSPF599.why is that? Typos? Redistribute static metric-type 1 subnets route-map into-ospf Lets say a route is learned through both OSPF processes, what happens then.? What about the RIB? Are there effectively separate routing tables? Why would someone run multiple OSPF processes on the same router?Īre there two SEPARATE databases that are established, one for each process?
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